/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.result.method.annotation;

import reactor.core.publisher.Mono;

import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.core.MethodParameter;
import org.springframework.core.ReactiveAdapterRegistry;
import org.springframework.lang.Nullable;
import org.springframework.web.reactive.BindingContext;
import org.springframework.web.reactive.result.method.SyncHandlerMethodArgumentResolver;
import org.springframework.web.server.ServerWebExchange;

/**
 * An extension of {@link AbstractNamedValueArgumentResolver} for named value
 * resolvers that are synchronous and yet non-blocking. Sub-classes implement
 * the synchronous {@link #resolveNamedValue} to which the asynchronous
 * {@link #resolveName} delegates to by default.
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 */
public abstract class AbstractNamedValueSyncArgumentResolver extends AbstractNamedValueArgumentResolver
        implements SyncHandlerMethodArgumentResolver {

    /**
     * Create a new {@link AbstractNamedValueSyncArgumentResolver}.
     *
     * @param factory  a bean factory to use for resolving {@code ${...}}
     *                 placeholder and {@code #{...}} SpEL expressions in default values;
     *                 or {@code null} if default values are not expected to have expressions
     * @param registry for checking reactive type wrappers
     */
    protected AbstractNamedValueSyncArgumentResolver(
            @Nullable ConfigurableBeanFactory factory, ReactiveAdapterRegistry registry) {

        super(factory, registry);
    }


    @Override
    public Mono<Object> resolveArgument(
            MethodParameter parameter, BindingContext bindingContext, ServerWebExchange exchange) {

        // Flip the default implementation from SyncHandlerMethodArgumentResolver:
        // instead of delegating to (sync) resolveArgumentValue,
        // call (async) super.resolveArgument shared with non-blocking resolvers;
        // actual resolution below still sync...

        return super.resolveArgument(parameter, bindingContext, exchange);
    }

    @Override
    public Object resolveArgumentValue(
            MethodParameter parameter, BindingContext context, ServerWebExchange exchange) {

        // This won't block since resolveName below doesn't
        return resolveArgument(parameter, context, exchange).block();
    }

    @Override
    protected final Mono<Object> resolveName(String name, MethodParameter param, ServerWebExchange exchange) {
        return Mono.justOrEmpty(resolveNamedValue(name, param, exchange));
    }

    /**
     * Actually resolve the value synchronously.
     */
    @Nullable
    protected abstract Object resolveNamedValue(String name, MethodParameter param, ServerWebExchange exchange);

}
